﻿COSMICAL 
  PHYSICS 
  JEANS 
  185 
  

  

  lating 
  itself 
  spontaneously, 
  the 
  energy 
  produced 
  in 
  the 
  process 
  being 
  

   set 
  free 
  as 
  radiation. 
  Its 
  rate 
  of 
  generation 
  of 
  energy, 
  as 
  estimated 
  

   from 
  the 
  luminosities 
  of 
  the 
  youngest 
  stars, 
  is 
  of 
  the 
  order 
  of 
  1,000 
  

   ergs 
  per 
  gram 
  per 
  second. 
  As 
  the 
  annihilation 
  of 
  1 
  gram 
  of 
  matter 
  

   produces 
  9 
  X 
  10-° 
  ergs 
  of 
  energy, 
  the 
  matter 
  must 
  have 
  a 
  " 
  period 
  of 
  

   decay" 
  of 
  OXIO^'' 
  seconds, 
  or 
  about 
  30,000 
  million 
  years. 
  As 
  the 
  

   star 
  ages, 
  and 
  only 
  less 
  transformable 
  matter 
  remains, 
  the 
  period 
  of 
  

   decay 
  is 
  correspondingly 
  lengthened. 
  The 
  matter 
  in 
  the 
  sun, 
  radiat- 
  

   ing 
  2 
  ergs 
  per 
  gram 
  per 
  second, 
  must 
  have 
  a 
  period 
  of 
  decay 
  of 
  

   15,000,000 
  million 
  years. 
  It 
  is 
  these 
  periods 
  of 
  decay 
  which 
  deter- 
  

   mine 
  the 
  rates 
  of 
  evolution 
  and 
  length 
  of 
  life 
  of 
  the 
  stars. 
  Broadly 
  

   speaking, 
  a 
  star 
  lasts 
  as 
  long 
  as 
  the 
  atoms 
  of 
  which 
  it 
  is 
  composed, 
  

   and 
  the 
  lives 
  of 
  these 
  atoms 
  are 
  constants 
  of 
  nature. 
  

  

  We 
  notice 
  that 
  the 
  periods 
  of 
  decay 
  of 
  stellar 
  atoms 
  are 
  long 
  

   compared 
  xviih 
  the 
  periods 
  of 
  ordinary 
  radioactive 
  decay, 
  suggesting 
  

   that 
  the 
  radioactive 
  elements 
  are 
  mere 
  transitory 
  formations 
  in 
  the 
  

   evolution 
  of 
  the 
  elements. 
  

  

  THE 
  CRITICAL 
  CENTRAL 
  TEMPERATURE 
  

  

  A 
  group 
  of 
  stars 
  selected 
  for 
  having 
  approximately 
  equal 
  masses 
  — 
  

   as, 
  for 
  example, 
  the 
  sun, 
  Procyon, 
  and 
  the 
  two 
  components 
  of 
  a 
  Cen- 
  

   tauri 
  — 
  might 
  be 
  expected 
  a 
  priori 
  to 
  have 
  very 
  different 
  rates 
  of 
  

   generation 
  of 
  energy, 
  with 
  the 
  result 
  that 
  the 
  stars 
  would 
  have 
  very 
  

   different 
  surface 
  temperatures 
  and 
  also 
  very 
  different 
  central 
  tem- 
  

   peratures. 
  Indeed, 
  on 
  first 
  approaching 
  the 
  question, 
  the 
  whole 
  

   range 
  of 
  temperatures 
  from 
  zero 
  to 
  infinity 
  would 
  seem 
  to 
  be 
  open 
  

   for 
  each 
  of 
  these 
  quantities. 
  Yet 
  in 
  actual 
  fact 
  the 
  surface 
  tem- 
  

   peratures 
  of 
  the 
  four 
  stars 
  mentioned, 
  as 
  also 
  of 
  all 
  stars 
  of 
  the 
  same 
  

   mass, 
  lie 
  within 
  the 
  narrow 
  range 
  between 
  3,700 
  and 
  8,300 
  degrees; 
  

   their 
  central 
  temperatures 
  probably 
  lie 
  within 
  the 
  range 
  from 
  15,- 
  

   000,000 
  to 
  100,000,000 
  degrees. 
  For 
  stars 
  of 
  other 
  masses 
  the 
  limits 
  

   are 
  different, 
  and 
  are 
  substantially 
  wider 
  for 
  stars 
  of 
  great 
  mass. 
  

   But 
  the 
  stars 
  of 
  any 
  definite 
  mass 
  always 
  show 
  a 
  definite 
  upper 
  

   limit 
  of 
  temperature, 
  both 
  for 
  the 
  surface 
  temperature 
  and 
  for 
  the 
  

   central 
  temperature. 
  These 
  limits 
  are 
  never 
  exceeded, 
  but 
  the 
  ma- 
  

   jority 
  of 
  stars 
  of 
  the 
  particular 
  mass 
  in 
  question 
  seem 
  to 
  crowd 
  

   toward 
  them. 
  The 
  existence 
  of 
  one 
  limit, 
  of 
  course, 
  implies 
  the 
  exist- 
  

   ence 
  of 
  the 
  other, 
  and 
  it 
  seems 
  likely 
  that 
  the 
  limit 
  to 
  the 
  central 
  

   temperature 
  is 
  the 
  more 
  fundamental. 
  Stars 
  having 
  the 
  same 
  mass 
  

   as 
  our 
  sun 
  never 
  have 
  central 
  temperatures 
  higher 
  than 
  80,000,000 
  

   degrees, 
  while 
  the 
  majority 
  have 
  central 
  temperatures 
  not 
  very 
  far 
  

   below 
  80,000,000 
  degrees. 
  For 
  stars 
  20 
  times 
  as 
  massive 
  as 
  our 
  sun, 
  

   the 
  corresponding 
  limit 
  is 
  probably 
  somewhere 
  about 
  300,000,000 
  

  

  